Constraints on transient glacier slip with ice-bed separation

Abstract

Glacier slip facilitates fast glacier flow and modulates sea-level rise, but empirical constraints on slip-controlling processes at relevant scales are limited. Modern slip rules often assume debris-free basal ice and process evolution within steady-state configurations, but basal ice is dirty and glacier systems regularly experience transient forcings, particularly when surface melting occurs. Seismicity (ice-quakes) generated by basal slip provide a window on subglacial dynamics, but ice-quake activity is often too sparse to resolve diagnostic trends at scales relevant to slip processes. Here we overcome this natural limitation with a rich ice-quake catalog from an alpine glacier with sub-diurnal and decametric resolution. We find characteristic trends between system hydrology, slip, inferred subglacial stress states, and seismicity that are inconsistent with steady-state frameworks. Specifically, ice-quake occurrence is elevated at times when slip decelerates and subglacial cavities are likely large: a configuration favoring reduced drag. This is reconciled by including debris-bed contact phenomena that enhance drag under these conditions, partially stabilizing glacier slip while favoring seismogenesis. Our observations provide empirical validation for this revised framework and advance our understanding of subglacial physical processes.